A variety of devices have or may require the use of a transmission such to vary the parameters of speed and torque between the input and output. In many instances, such a transmission is desired to be relatively small and lightweight, and be capable of effecting relatively small increments of changes between the input and output ratio. Human powered vehicles are one example of such devices. Human-powered vehicle transport has had a relatively long history, and the vehicles produced have taken a variety of forms, and have employed a number of different transmissions or drive mechanisms. Among the different human-powered vehicle types, the bicycle has perhaps met with the most widespread use due its relatively compact and lightweight form, maneuverability, and efficiency in converting human muscle power to forward movement. Given the typical slope terrain conditions encountered by the human powered vehicle, a necessity has arisen to provide a drive system providing rider-selectable input-output drive ratios. Such a drive system allows the rider to adjust peddling speed and torque to best accommodate desired vehicle speed and terrain conditions, and a variety of means for such drive mechanisms have been proposed in the conventional art.
Perhaps the most common multi-ratio drive is provided by a front sprocket driven through foot pedals pivotally linked to cranks, and a rear sprocket cluster or cassette connected to the rear drive wheel. Typically, a loop-chain links the front and rear sprockets, and a rear derailleur provides means for the rider to select a given sprocket from the rear sprocket cluster to engage with the chain. In some cases, more than one front sprocket will be provided, forming thereby a front sprocket cluster; a second front derailleur provides means for the rider to select a given sprocket from the front sprocket cluster to engage with the chain. In a typical multi-ratio bicycle drive between 5 and 10 separate sprockets comprise the rear sprocket cluster, and between 1 and 3 separate sprockets comprise the front sprocket cluster, providing thereby a drive having between 5 and 30 user-selectable combinations.
The typical multi-ratio drive employing a chain, front and rear gear clusters, and derailleurs is perhaps the most common bicycle drive means in contemporary use. Unfortunately, such typical drives suffer from a number of disadvantages, including a relatively high mechanical complexity, weight, and unreliability. For example, the derailleur is a fairly sensitive mechanism, requiring precise adjustment, and which may easily become misaligned. Damage or misalignment may occur as the derailleurs are exposed to the weather, and are also vulnerable should the bicycle fall over. Should misalignment occur, the chain may become misplaced from the drive system, and may jam other moving parts of the bicycle; this condition may prove hazardous as the speed or direction of the vehicle may be abruptly altered. Another primary drawback of such typical drives is the steps between the user-selected ratios. The selected ratio is often not ideal for the given circumstances of terrain and available input power. As well, the variety of ratios offered by a combination of multiple front and rear sprockets may be confusing to all but the most experienced riders, causing the need for much trial and error to select the most suitable ratio. It is noted that while a given drive using both front a rear derailleurs may provide up to 30 user-selectable combinations, all such combinations will not produce a substantially different ratio than the others. Therefore, the number of distinct gear ratios is typically around 70% of possible gear ratios, and the number of easily usable distinct gear ratios is typically around 50% of possible gear ratios.
A rider may ride on relatively flat terrain one day, and relatively hilly terrain the next. The typical multi-gear and derailleur drive system may include a relatively wide range of gearing to accommodate these varied conditions. However, such inclusion of such multiple gearing is less than optimal as many of the gears contribute to added weight, and are not used in all conditions. Competitive cyclists may elect to change the gear sprockets to best address the terrain conditions of a given racecourse. However, this is a fairly involved procedure, and is not practical for the ordinary cyclist.
The typical multi gear and derailleur drive system is also relatively heavy. Weight is an important factor in bicycle drive systems, particularly for performance and competitive cycling. A number of components used in the typical multi sprocket and derailleur drive system individually and collectively contribute to the overall system weight. These typically include a link steel chain, front and rear derailleurs, the rear sprockets or cassette, and the front sprockets or chainrings.
A number of attempts have been proposed to improve upon the typical multi-ratio drive employing a chain, front and rear gear clusters, and derailleurs. A typical type is often referred to as a hub gear. Such drives incorporate multiple gears and means to select between gears that are housed within the rear wheel hub mechanism. Unfortunately these drives are typically heavier, less efficient, and offer fewer selectable gear ratios than the typical multi sprocket and derailleur drive system.
Attempts have been made to overcome the primary disadvantage of the steps between ratios in drives commonly referred to as “stepless” or “continuously-variable”. Of the many types of proposed stepless drives, the majority suffer from a high degree of mechanical complexity, relatively high weight, a necessity for frequent maintenance and adjustment, and an inability to be fitted into, or to be retrofitted into a common bicycle frame and cooperate with other typical components. One such drive (see e.g., U.S. Pat. No. 8,167,759, Pohl et al., 2012) uses a plurality of traction planets, made able to rotate about a tiltable axis to provide a continuously variable transmission useable in various devices, including bicycles.
A seemingly straightforward means of accomplishing a stepless drive for human powered vehicles would be to provide a drive means able to vary the effective diameter of the driven pulley or sprocket. Drives of this type have been proposed in the conventional art, with a typical type containing a plurality of coordinated radially-disposed sprocket segments. Unfortunately, drives in the conventional art using such means are unable to provide a simple method to coordinate the radial displacement of the plurality of sprocket segments such to change the effective sprocket diameter. Of these types of drives, some propose to provide an “automatic” drive; one such example is given in U.S. Pat. No. 3,995,508, Newell, 1976, which discloses a drive using a plurality of sprocket segments spring-biased to the largest effective diameter, and which under increased input torque load will automatically overcome the spring bias to decrease the effective diameter. While an automatic drive of this type may offer convenience for novice and undemanding riders, those more skilled or desiring to compete in cycling sports will desire greater control of the drive ratio and input torque.
In another example, U.S. Pat. No. 4,938,732, Krude, 1990, discloses a stepless drive providing operator control over the input output ratio. This transmission provides a variable diameter pulley comprised of pulley segments that may be moved axially in the radial direction. Means to coordinate the pulley segments is provided by a first pair of disks disposed on one side of the pulley segments, and a second pair of disks disposed on the other side of the pulley segments. Each disk comprising each disk pair has radially disposed arcuate slots, and the arcuate slot sense of the pair is opposed, and with the space provided by the overlap condition able to accept a pin formed into the pulley segment. Each pair of disks is made able to rotate relative to the other, and to cause the space provided by the overlap condition to move in the axial direction. The means to control the effective diameter is first input by an actuator placed concentrically with the axis of rotation of the disks, and this motion is transferred to the radial direction with a plurality of actuator pins. The inclusion of four total disks, combined with the necessity to transfer actuation control from the rotational axis to the radial axis results in considerable complexity in the mechanism, a relatively high part count, and added weight. It will also be noted that the pulley segment engages with the space provided in the pair of opposed sense arcuate slots is round, and therefore this arrangement of elements does not constrain the pulley segments to the radial direction. As a result, other means need to be added to provide such constraint. Engagement between the pulley segments and drive belt is provided by contact friction, and no other means to provide higher levels of contact sliding resistance are incorporated.
In yet a further example, U.S. Pat. No. 3,956,944, Tompkins, 1976, discloses a variable ratio chain sprocket having a plurality of chain engaging segments slidingly affixed between a first pair of disks fixed to an axle having radially-deposed arcuate slots, and a second pair of disks, able to rotate freely about said axle having radially disposed straight slots. Each chain engaging segment is slidingly engaged with a respective straight and arcuate slot on a first side, and with a straight and arcuate slot on an opposed side. With the forgoing interrelationship of elements, the rotational displacement of the first pair of disks relative to the second pair of disks will cause the chain engaging segments to move in a radial fashion and thereby present varied effective sprocket diameters. A spring links the first pair of disks with the second pair of disks. When sufficient torque is applied to the input, the spring is stretched, and the rotational displacement of the first pair of disks relative to the second pair of disks is effected. As such this invention is of the “automatic” type described by Newell, and therefore suffers from the inability to provide the user means to control the input-output ratio directly as no actuator and control means is provided to accomplish this function. In addition, the invention requires inclusion of four total disks. Each pair of disks contacts each other that may cause considerable friction or the accumulation of dirt between them. Finally, the invention is only able to function with use of an endless chain, and does not give provision for use with an endless belt.
In a final example, GB19800034485 1980 1027, Deal, 1981, discloses a variable diameter sprocket having a plurality of sprocket segments disposed in a radial pattern slidingly affixed between a first disk fixed to an axle having radially-deposed arcuate slots, and a second disk, able to rotate freely about said axle having radially disposed straight slots. Each chain engaging segment is slidingly engaged with a respective arcuate slot on a first side, and with a straight slot on an opposed side. With the forgoing interrelationship of elements, the rotational displacement of the first disk relative to the second disk will cause the chain engaging segments to move in a radial fashion and thereby present varied effective sprocket diameters. A plurality springs link the first pair of disks with the second pair of disks. When sufficient torque is applied to the input, the springs are stretched, and the rotational displacement of the first and second disk is effected. As such this invention is of the “automatic” type described by Newell and Tomkins, and similarly suffers from the inability to provide the user means to control the input-output ratio directly as no actuator and control means is provided to accomplish this function. The invention is only able to function with use of an endless chain, and does not give provision for use with an endless belt.
In summary, it may be seen that conventional art variable ratio drives incorporated into human powered vehicles, such as bicycles, have a number of defects including complexity and unreliability, lack of intuitive ease of use, relatively high weight, and the inability to easily be retrofitted into existing bicycle frames and make use of and interface with other common bicycle components.
While the preceding discussion has given focus to the application of the continuously variable transmission to human powered vehicles in general, and bicycles in particular, it can be seen by one of ordinary skill the art, that the continuously variable transmission can have a wide range of applications to other powered vehicles, machines, and devices. As a first example, it will be noted that most vehicles encounter varying terrain conditions that necessitate adjustment of the parameters of speed and torque between the input and output. A low gear may be required to climb a steep slope, and a high gear may be required to increase the vehicle speed. Most all types of input power, such as an internal combustion engine, have limitations on torque, power, and speed, and may operate most efficiently in a fairly narrow band of such parameters. The input-output ratios provided by a transmission provide means to maintain the relative efficiency of the engine operation. Conventional multi-gear transmissions attempt to maintain such efficiency, but are limited to the number of gears in the transmission, and therefore only approximate the more ideal ratio needed at any given point in time. In contrast, a continuously variable transmission has infinitesimal steps between the input-output ratios, and thereby has means to provide a more ideal ratio needed at any given point in time.
As a second example, a number of machines or devices, such as a drill press, lathe, milling machine, or, windmill, to name but a few examples, also require varying speed, power, and torque parameters between the input and output. In typical machining operations, for example, various factors such as cutting head, feed rate, lubricant, plunge rate, and metal type must be calibrated with the speed and torque of the tool output. A tool, such as one having robotic control, may encounter variations of these factors in relatively quick secession, and must have the ability to adjust input-output ratios accordingly.
What is needed then is a continuously variable transmission that is relatively inexpensive to purchase and maintain, that has a simple and highly controllable drive mechanism, that limits the number of steps between drive ratios, that provides intuitive ease of use, is relatively light in weight, that may be fitted or retrofitted into common machine and vehicle frames and formats, and provides an efficient transfer of input power to an output. In addition, it is often found to be desirable to obtain information about the operation and conditions of a machine. Such information may include altitude, inclination, temperature, distance, speed, torque, gear ratio, and other inputs. Therefore, a drive mechanism that easily cooperates with an onboard computer, can wirelessly communicate with external devices, and extend the range of data collection would be desirable to those operating or managing such machines.